The present invention relates to a method and apparatus for cutting sheet material with a closed loop control. More particularly, the present invention relates to an automatically controlled machine for cutting sheet material with a cutting tool such as a reciprocating blade and means for sensing a cutting parameter during cutting in order to adapt the automatic controls to existing conditions and improve overall performance.
It is well known to use automatically controlled cutting machines for cutting limp sheet material used in garments, upholstery, and other items. Such machines conventionally derive information defining the articles or patterns to be cut from a marker. The marker is a closely arranged array of pattern pieces in positional relationship for cutting from a layup of sheet material. The contours of the pattern pieces which define the cutting paths to be followed by the cutting blade are the raw data which are utilized by the automatically controlled cutting machine in guiding the cutting blade, and such data is translated by the machine into machine commands by appropriate hardware. For example, the marker may be digitized to reduce the contours to point data and then the point data is processed through a computer or data processor to generate machine commands which translate the cutting blade and sheet material relative to one another. The marker data may be preprocessed and recorded for subsequent use in a cutting machine or the data may be processed during the cutting operation.
Other information systems may be used for acquiring and then using the raw data. For example, line followers may be used to transpose marker data from graphic material or templates, and the data can then be processed by other hardware which may include either analog or digital equipment, for example.
In most prior art cutting systems which are automated, the cutting operation is substantially fixed by pre-established programs and the marker data. Thus, the maneuvering of the cutting blade along a desired line of cut is controlled in accordance with relatively standard routines that have proven in general to be suitable for many cutting conditions but not necessarily all cutting conditions nor unanticipated conditions. For example, the standard cutting operation may not be suitable or may produce poor results with certain types of limp sheet material, with layups of substantial depth and even within a single layup displaying different cutting characteristics under different conditions. In U.S. Pat. No. 3,803,960, a system is disclosed which constitutes an improvement over the earlier systems in that some degree of flexibility in the cutting program is provided by allowing the person digitizing the marker to call for special cutting blade maneuvers, such as yawing and reduced feed rates, under limited circumstances. Yawing refers to the rotation of a cutting blade away from a position tangent to a cutting path or parallel with the path velocity vector of the blade. Still, a more flexible and more responsive control system is desirable.
Accordingly, it is desirable to have an automatic cutting machine which is responsive to different cutting conditions as they occur in a cutting operation. By adjusting or initiating special control functions during the course of the cutting operation in response to a sensed condition, the overall performance of an automatically controlled cutting machine and the quality of the resulting product will be improved.
A closed loop control system for an automatically controlled cutting machine is disclosed in U.S. Pat. No. 3,848,490 having the same assignee as the present invention. In the prior art patent, a pressure sensor is utilized to detect previous cuts in the sheet material in the immediate vicinity of the cutting blade, and corrective adjustment in the automatic blade control mechanism is made in response to feedback signals generated by the pressure sensor. The corrective adjustment may reduce the feed rate as the cutting blade passes the previous cut or the blade may be given yaw commands which rotate the blade slightly out of alignment with the desired cutting path in the same region.
It is believed that more meaningful information concerning the cutting operation can be derived continuously from the interaction of the cutting blade and sheet material and corrective adjustment and other operations can be regulated accordingly. It is, therefore, a general object of the present invention to provide a closed loop method and apparatus for controlling a cutting blade by sensing one or more cutting parameters as the blade advances in cutting engagement with the material and then utilizing the parameters to modify the cutting operation.